Yeah. There is no central server for searches, your search results depend on which parts of the Fediverse your server sees.
It sounds like infosec.exchange has connections that are more relevant to your searches than mastodon.social, and it's one reason why it's good to join a server that matches your interests.
If you want a detailed explanation, here's a list of how a server "sees" the Fediverse:
https://fedi.tips/which-posts-and-accounts-can-i-see-from-my-server/